The use of light-readable (particularly laser-readable) or stylus-readable information has provided new products in the market place for information retrieval. The most successful form of this technology exists in the format of video discs. These are flat, circular sheets having information encoded thereon in a pattern of grooves which are light-readable or stylus-readable on at least one surface of the disc. The encoded information on the discs is translatable to electronic information which can be projected in visual form on a cathode screen. A popular format for this technology exists as video discs which contain encoded information that can be viewed on television screens in the form of movies, plays, business presentations, and the like.
Many different variations in the systems are known in the art, and substantial volumes of literature have been published disclosing the various techniques used to manufacture and read information stored in this manner. For example, U.S. Pat. No. 3,855,426 discloses a video disc recording and optical playback system therefore in which a beam of radiation is used to read information off an information track. It is to be noted that in this and other light-readable systems, it is common to include parallel tracks, one containing information to be converted to a visual signal and a second track used to assist the optical playback system in tracking the information properly. U.S. Pat. No. 4,126,726 also discloses a two-sided radiation-readable information carrying disc. U.S. Pat. application Ser. No. 117,467, filed Feb. 1, 1980 in the name of Donald J. Kerfeld discloses a process for forming information carrying discs which can be read either by optical or stylus means.
A number of differing methods are used to form the information carrying disc. Some of the earliest methods attempted direct impression of the information carrying surface structure into thermoplastic polymeric blanks as is still presently done in the phonograph record art. This type of process is shown in U.S. Pat. No. 3,658,954. Subsequent improvements in the processes of manufacturing video discs used liquid compositions which could be heat cured or radiation cured in molds to provide the information carrying structure. These types of processes are shown, for example, in U.S. Pat. Nos. 4,126,726; 4,272,574; 4,017,581; 4,130,620; 3,795,534 and 4,124,672.
A broad spectrum of compositions has been disclosed for use in the manufacture of the cured information carrying layer. Such various materials as thermoplastic vinyl resins (U.S. Pat. No. 3,658,954), acrylics, epoxies and other polymerizable materials (U.S. Pat. No. 4,124,672), epoxy-terminated silanes (U.S. Pat. No. 4,304,806) and polyacryloyl-containing heterocyclic monomers (U.S. Pat. No. 4,296,158) and photopolymerizable laquers (U.S. Pat. No. 4,126,726) have been shown in the literature.
In spite of the broad and extensive disclosure of structures, processes and compositions useful in the formation of information carrying substrates, problems still exist in the art. In particular, compositions used in forming the information carrying structure of the discs have shown problems with regard to adherence to the substrate onto which the information carrying structure is formed, extensive shrinkage during molding, and internal stress marks.